A model to explain both variation and change in rates of place-to-place migration is to be developed. The model proposes that social networks linking together members of separate populations are a major determinant of migration rates, in themselves, and that social ties increase or reduce the extent to which other important factors, such as economic opportunity and distance, affect migration rates. Important potential contributions include increasing the predictability of migration patterns and accounting for instability over time and groups in effects of important migration determinants. The causal model will be tested by multiple regression analysis of rates of migration within 2450 interstate migration streams during two time periods (1965-70 and 1975-80) and of change in interstate migration rates between 1965-70 and 1975-80. Separate tests will be conducted for each of eight age-race prior migration status-specific subgroups for each single-period cross-section and the change period, using data from the 1970 Public Use Sample and the 1980 Public Use Microdata of the U.S. Census.